German patent publication 197 34 112 discloses a method and an arrangement for controlling the drive unit of a vehicle. In this known solution, a drive torque is continuously computed in accordance with resistance torques which drive torque is maximally transmittable to the roadway under the given conditions. If a tendency to rotate without adherence to the roadway occurs on at least one drive wheel of the vehicle, the drive unit of the vehicle is so influenced (especially a control quantity such as the torque of the drive unit is reduced) that the maximally transmittable torque is adjusted. Thereafter, the drive unit is controlled in the context of a drive slip control and, in this way, the tendency of the at least one drive wheel to slip is reduced.
In many cases, this procedure has lead to a satisfactory solution. However, it has been shown, especially in very powerful engines, that this procedure is not optimal. Because of the power capability of the drive unit, a drive slip control intervention is introduced very rapidly when a driver command is present for high power. Because of the slippage of the drive wheels and the early drive slip control intervention, an unsatisfactory driving performance results because of the effect on the acceleration of the vehicle.
The limiting of the increase of at least one control quantity of the drive unit (when the driver outputs a control value for which an instability of the drive wheels is to be expected) leads to a finer metering of the control of the drive unit as well as to a control of the drive unit which is satisfactory with respect to actual requirements. This control quantity is preferably a control quantity, such as torque of the drive unit. The occurring drive wheel slip is reduced and even avoided in ideal cases and is shorter in time when it occurs. In this way, the acceleration capability of the vehicle is improved while simultaneously increasing the stability because the occurrence of the drive wheel slip is reduced.
It is especially advantageous that the increase limiting only takes place when the operator input is greater than a threshold value derived from the maximally transmittable value. In the stable range, the full performance is available to the operator, whereas a limiting of the increase takes place only with inputs above the maximally transmittable value. This increase limiting is optimized with respect to acceleration and stability.
A limiting of the increase takes place above the threshold value. In the determination of this threshold value, it is also advantageous to consider a stored value which corresponds to the input for the control of the drive unit for which a previous tendency toward slippage of the drive wheels and therefore the previous slip control intervention has occurred. In this way, a further improvement of the driving performance is achieved.